Problem: Let N be a positive odd number.

There are N coins, numbered 1, 2, \ldots, N. For each i (1 \leq i \leq N), when Coin i is tossed, it comes up heads with probability p_i and tails with probability 1 - p_i.

Taro has tossed all the N coins. Find the probability of having more heads than tails.

Constraints

* N is an odd number.
* 1 \leq N \leq 2999
* p_i is a real number and has two decimal places.
* 0 < p_i < 1

Input

Input is given from Standard Input in the following format:


N
p_1 p_2 \ldots p_N


Output

Print the probability of having more heads than tails. The output is considered correct when the absolute error is not greater than 10^{-9}.

Examples

Input

3
0.30 0.60 0.80


Output

0.612


Input

1
0.50


Output

0.5


Input

5
0.42 0.01 0.42 0.99 0.42


Output

0.3821815872

Solution (in JAVA):

Solution:

import java.util.Scanner;


public class Main {

	/**
	 * @param args
	 */

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		double[][] ans = new double[n+1][n+1];
		ans[0][0]=1;
		for (int i=0;i<n;i++) {
			double p = sc.nextDouble();
			ans[i+1][0]=ans[i][0]*(1-p);
			for (int j=0;j<n;j++) {
				ans[i+1][j+1]=ans[i][j]*p+ans[i][j+1]*(1-p);
			}
		}
		
		double out = 0;
		for (int i=(n+1)/2;i<=n;i++) {
			out += ans[n][i];
		}
		System.out.println(out);
	}

}